Goldenseal, Kava Do Not Interfere With Digoxin

MEMPHISResearchers at the University of Tennessee Health Science Center here found goldenseal and kava kava do not appear to affect how the body uses digoxin (cardiac glycoside) in the form of Lanoxin® (GlaxoWellcome). Twentyhealthy volunteers were randomly assigned to receive 3,210 mg/d of standardizedgoldenseal (Hydrastis canadensis) or 1,227 mg/d kava (Piper methysticum) for 14 days, followed by a 30-day washout period. Participants were also randomized to receive rifampin (600 mg/d for seven days)and clarithromycin (1,000 mg/d for seven days) as positive controlsfor p-glycoprotein (P-gp) induction and inhibition, respectively. Digoxin, in 0.5 mg (Lanoxin) dosages, was given orally before and at the end of eachsupplementation and control period. Serial digoxin plasma concentrationswere obtained over 24 hours and analyzed by chemiluminescent immunoassay. Comparisons of AUC_(0-3), AUC_(0-24), C_max, CL/F,and elimination half-life were used to assess the effects ofgoldenseal, kava, rifampin, and clarithromycin on digoxinpharmacokinetics. Rifampin produced significant reductions (p<0.01)in several chemical parameters while clarithromycinincreased them significantly (p<0.01).

With theexception of goldenseal's effect on C_max (14-percent increase), nostatistically significant effects on digoxin pharmacokineticswere observed following supplementation with either goldensealor kava. When compared to rifampin and clarithromycin,supplementation with these specific formulations of goldensealor kava did not appear to affect digoxin pharmacokinetics; and researchers suggest these supplements are not potent modulatorsof P-gp in vivo. The study was published in Drug Metabolism and Disposition (doi: 10.1124/dmd.106.012708, Nov. 2006).